Nowadays the use of laundry washing machines, both “simple” laundry washing machines (i.e. laundry washing machines which can only wash and rinse laundry) and washing-drying machines (i.e. laundry washing machines which can also dry laundry), is widespread.
In the present description the term “laundry washing machine” will refer to both simple laundry washing machines and laundry washing-drying machines.
Laundry washing machines generally comprise an external casing provided with a washing tub inside which there is a rotatable perforated drum in which the laundry is placed.
Some known washing machines comprise a water supplying system provided with two valves for supplying hot water and cold water into the washing tub, a temperature sensor which is arranged inside the washing tub and is designed for sensing the temperature of the water supplied from the valves into the washing tub, and a control device for controlling the opening or closing of each valve based on the sensed temperature by the temperature sensor.
Methods of controlling of the temperature of the supplied water based on the temperature sensor are accurate if the temperature sensor is in contact with the water. However, temperature sensor is typically arranged at a prefixed height above the bottom surface of the washing tub, and consequently it is temporarily not able to provide the correct water temperature during the first water wetting phase, wherein the supplied water takes time to reach a level in the washing tub to cause the temperature sensor to be immerged in the water. This condition may also happen during the following wetting phases, since water level can decrease because water is absorbed by the laundry, and also, if the machine is provided with a recirculation circuit, since because during recirculation water is drained from the bottom of the washing tub to be re-admitted into an upper region of the tub.
In both the above disclosed temporary conditions, the control of valves is therefore made according to a wrong/undetermined temperature, causing the temperature of the water supplied into the washing tub to be heavily different from the prefixed washing temperature of the washing program.
Of course, although temporary, filling water with wrong temperature into the washing tub, on the one side may cause the problem that laundry in the washing tub may be damaged, in particular if hot water is supplied to some kind of delicates laundry, and, on the other side, it requires an amount of time to be corrected, which may be longer than available time of the laundry wetting phase of the selected program, in particular in case of short program.